Wondering who it is that Mom talks to late at night

My Mom will be 90 in April.  She's lived with us for the past 10 years, has demensia and a few other health issues.  She's at the stage in her life where she has to have someone with her at all times.  She can't care for herself, needs help for all daily activities, and for the most part is nonverbal.  She'll mumble, and gets pretty load yelling at times, but hardly ever any understandable words.

Then, after she's been in bed at night for a while, she starts to talk in her sleep.  It sounds like she's having a conversation and you can only hear the one side of it.  She laughs.  She talks. It's hard to hear exactly what she's saying from where I am.  But, if I were to move closer, I'd likely wake her.  But, the sound of it reminds me so of the way she used to be.

This  conversation happens irregularly.  It could be a short one or a long one.  But, whoever she's talking to is very familier.

I often sit listening, trying to tell who it might be.  Is she dreaming or is she really talking with someone?  Could it be my Daddy, who passed over 30 years ago, or my brother, who passed at 40, 10 years ago?

Whoever it is, she always seems to enjoy the visit!  Wish they'd visit me, too!